How do we know what the sun is made of?

We all know that stars, for example the sun, are made up of particles such as hydrogen, but a friend challenged me recenlty asking HOW we know this, and I was forced to admit that I didn't know the answer....

so how do we know? probably a simple question, but my so-called "expertise" is more in the realm of computers and programming than physics and science

And if it's just the Sun (a.k.a. sol) your friend was asking about, then we can also say that we've collected bits of the Sun that it didn't want, and analysed them (the solar wind). We've also extracted 'old solar wind' from the soil on the Moon, and so we know what the Sun was 'exhaling' over a very long time (several billion years?)

I still don't understand how spectroscopy explains what the sun is made of. It seems to me that this only tells us what the sun is "burning" at the moment. How do we know that the sun's core doesn't consists of different elements, perhaps packed into dense layers like the jawbreaker candy, so that eventually the sun will stop burning hydrogen and start "burning" something else?

Staff: Mentor

I still don't understand how spectroscopy explains what the sun is made of. It seems to me that this only tells us what the sun is "burning" at the moment.

No, emission and absorption spectra have nothing to do with what generates the heat, but rather what is giving off the heat. For example, a nebula such as the Horsehead nebula is back-lit by stars and glows red because it is made of Hydrogen and hydrogen's main emission lines are red. For the sun, the fusion happens in the core, but the emission and absorption spectra are from the matter on the surface and in the corona - and we can detect other elements besides hydrogen in the spectra.

How do we know that the sun's core doesn't consists of different elements, perhaps packed into dense layers like the jawbreaker candy, so that eventually the sun will stop burning hydrogen and start "burning" something else?

Actually, it will eventually start burning (fusing) other things, such as helium. You can't directly observe what goes on inside a star, but by watching them evolve and measuring the amounts of certain elements, and applying nuclear physics you can deduce what must be happening.

I still don't understand how spectroscopy explains what the sun is made of. It seems to me that this only tells us what the sun is "burning" at the moment. How do we know that the sun's core doesn't consists of different elements, perhaps packed into dense layers like the jawbreaker candy, so that eventually the sun will stop burning hydrogen and start "burning" something else?

True, but there are two things that you can do.....

1) you can run computer models assuming that the sun is made up of X, Y, and Z and see what happens, and try to match those models with observations

2) you can also do heliosesmiology. What happens is that you look at waves that you see on the surface of the sun, and since those waves go through the interior of the sun you can get a lot of detailed information about pressure and density which you they match with your computer models.

2) you can also do heliosesmiology. What happens is that you look at waves that you see on the surface of the sun, and since those waves go through the interior of the sun you can get a lot of detailed information about pressure and density which you they match with your computer models.

I was going to mention helioseismology, but you beat me to it! This is a very interesting field of research, in my opinion. There's a great article about using the principles of helioseismology to study other stars here.

Indeed, but it is important to note that the only observable that tell us what is happening inside the star is the neutrino! Although it is hard task to detect them.

Helioseismology (i.e. seeing how pressure waves go through the sun) tells you a lot about what is going on inside the sun just like most of what we know about the earth comes from studying how earthquake waves go through the earth.

As far as the solar neutrino problem, there were two possibilities. Either there was something strange going on in the middle of the sun or there was something strange going on with neutrinos. Helioseismology pretty much ruled out something weird happening in the center of the sun. When you see how pressure waves go through the sun, you end up with densities, pressures, and temperatures that are exactly what the computer models predict.

Helioseismology (i.e. seeing how pressure waves go through the sun) tells you a lot about what is going on inside the sun just like most of what we know about the earth comes from studying how earthquake waves go through the earth.

As far as the solar neutrino problem, there were two possibilities. Either there was something strange going on in the middle of the sun or there was something strange going on with neutrinos. Helioseismology pretty much ruled out something weird happening in the center of the sun. When you see how pressure waves go through the sun, you end up with densities, pressures, and temperatures that are exactly what the computer models predict.

Was not the neutrino problem solved? With the oscilation between their 3 flavors? Or you just mentioned that there was the solar neutrino problem...?

I really do not know anything about helioseismology, how it works and it's results. Does the observations lead to something different predicted from the models?